Dog dander is a common cause of indoor allergy with symptoms including rhinitis, conjunctivitis, bronchial inflammation and asthma. Dog allergens can be detected not only in houses where dogs are kept as pets but also in other places such as schools and day care centres where dogs are not present on a regular basis (1).
Allergy to dog is accompanied and dependent of sensitization to proteins released from dog hairs and dander. In cases of suspected allergy to dog, the clinical investigation includes assessment of sensitization by skin prick or specific IgE antibody measurement using extract of dog hair and/or dander. A laboratory immunoassay for specific IgE, such as a Phadia ImmunoCAP, can detect most cases of sensitization to dog using natural dog dander extract due to favourable assay conditions and a large solid phase available for allergen attachment.
Dog hair and dander extracts contain a complexity of allergenic and non-allergenic proteins (2, 3). Three dog allergens have so far been identified and studied in detail: Can f 1, Can f 2 and Can f 3. Can f 1, a member of the lipocalin protein family, with reported molecular weight of 21-25 kD, was first purified by de Groot et al. (4) and later cloned and expressed as a recombinant protein (5). Can f 2 belongs to the same protein family but is a protein distinct from Can f 1 (4, 5). Can f 3, dog serum albumin, is a relatively conserved protein demonstrating extensive cross-reactivity to other mammalian albumins (6).
Of the known dog allergens, Can f 1 is the most important, binding IgE antibodies from approximately half of dog allergic subjects (7). About 20% of dog allergic subjects display IgE binding to Can f 2 but most of these are also sensitized to Can f 1. Although 30-40% of adult dog allergic individuals may show IgE binding to Can f 3 (2, 8), the specific clinical relevance of mammalian serum albumins is uncertain.
It has been known for a long time that major allergens relevant to allergy to rodents, such as mice and rats, are present in the animals' urine and these have been isolated and extensively characterized (9-13). IgE antibody binding activity has also been reported to exist in urine of other animals, including cats and dogs (14), but no allergen has been purified from urine of these animals and characterized at a molecular level.